The purpose of this work is to examine the chemical, biological and immunological properties of histocompatibility antigens (H-2) and tumor specific transplantation antigens (TSTA). The approach is to purify the molecules expressing these antigens and determine their properties at each stage of the purification. These properties include: 1) Ability to induce in vivo transplantation rejection, 2) ability to induce an in vivo humoral response, 3) ability to react with autologous and heterologous antisera, 4) chemical properties, 5) ability to interact with lymphoid cells in vitro. The rationale for this approach is that through purification of these antigens from a single source, one can determine the relationships, if any, between the H-2 antigens and TSTA. Furthermore, any unusual structural properties of H-2 and TSTA from tumor cells, when compared to the structure of their counterparts from other tumors and normal cells, may shed light on the molecular basis for the biological activity of these antigens. Finally, when they are purifed, the chemical structure of these antigens will aid in the understanding of the organization of the genes which encode them.